Unfortunately this is a very common automotive dealership scam.
Dealerships will often hook customers in this way by selling them a car and then calling them 2 to 3 days later (typically right as the return period in their state ends) for re-negotiation of purchase financing.
That also gives the dealership a second crack at selling garbage like paint protection, undercoating, window etching, fabric protection, etc.
Does your contract have any language or wording that states purchase terms are “subject to finance approval” or “subject to credit approval”, or the like? Unless your agreement includes terms to that effect then whatever the dealer and you signed that day “is” the contract.
In theory, this kind of contract language means the dealership thinks you’re a nice person and is willing to let you drive their car off the lot even though financing isn’t settled. In theory they also have time to look around for the best possible deal. In reality no one will sell you a car without first setting rock-solid financing arrangements. In reality they’re going to find the deal that is most advantageous to them, and has the worst possible terms for you.
Tip for future use — Never under any circumstances sign any paperwork at a car dealership that somehow states financing is not final or complete when you walk out the door.
Walk into the store and politely insist on getting your second set of keys, no changes to the contract. Be polite but firm and do not budge on this.
If the dealership tries to keep you there, prevents or delays you leaving with the second keys (and original terms of the contact), or tries to wear you down until you agree to contract changes, call the police. Do not hesitate to call the police. Then call your local news station. Scammers will always back down in this circumstance.
As other answers have suggested, don’t ever use that dealership for any maintenance or other work on that car at all. And never buy anything else t